What if someone gets all champions m7

I think it's pretty doable if someone was so inclined, particularly if they are plat+ or so where their standards of play (for csing and so on which is relatively transferable between champs) make S ranks not that rare.

People can and did get rank 5 on a champ in a day. Then going from rank 5 to 7 in principle only takes 5 more games if they can get the required grades. Supposing people get their rank 5 in a a day of play, and then spend another whole day (instead of a couple hours) getting their S grades, that'd still be less than a year for rank 7 every champion if someone was so inclined.

edit: I do keep pushing the 'if so inclined' part though, since I feel like those with the skills to play every champion at an S grade level are probably more focused on actual ranked rather than mastery grinding.